In the brewing industry it is usual to use large quantities of carbon dioxide for producing or maintaining the carbonation of the brewed product, such as beer. Carbon dioxide is produced as a byproduct during the fermentation of the beer and for economic reasons it would be desirable to employ the carbon dioxide byproduct for the carbonation of the beer. However, the carbon dioxide byproduct is impure, often containing residual amounts of air, and it is necessary to purify the carbon dioxide before it can be used for carbonation or as an overgas. Thus in a brewing plant there is a demand for substantially pure gaseous carbon dioxide as a service to the beer producing process and there is also the concurrent production of carbon dioxide as a byproduct which must be purified.
In known brewing processes, the carbon dioxide byproduct, and the overgas which has been used to protect the brewed product from oxygen and contamination, are removed from the brewing plant and fed to an independent refrigeration circuit employing conventional refrigerating equipment. The carbon dioxide is then cooled and liquefied by the refrigerant in a known manner to produce substantially pure liquid carbon dioxide. The liquid carbon dioxide is then subsequently used to provide substantially pure gaseous carbon dioxide for use in the carbonation of the brewed product or as a substantially pure overgas.
In the conventional plant the production of substantially pure gaseous carbon dioxide from substantially pure liquid carbon dioxide is carried out in a first vessel by using energy from steam or electricity to evaporate the liquid carbon dioxide. The purification of the byproduct is carrid out in a separate second vessel, again using energy, by liquefying impure carbon dioxide to provide substantially pure liquid carbon dioxide. Each of those steps requires the input of energy and consequently the costs of running the plant are high.
Normally, in brewing plants the liquefaction of the impure byproduct is carried out on relatively pure feeds which have been pre-purified by purging impurities from the gases at the start of fermentation. There is a substantial loss of CO.sub.2 from this purging.
The present invention relates to a process which can purify the carbon dioxide byproduct "on site" so that the purified gaseous carbon dioxide is ready for use in carbonation of the brewed product or for use as an overgas which employs less energy than the conventional brewing plant for the production of substantially pure gaseous carbon dioxide for use in the brewing plant, and which can be used to purify gaseous carbon dioxide containing relatively large amounts of impurities.